Lumbar spinal stenosis, for example, is characterized by a tightening of or decrease in the cross-sectional diameter of the spinal canal and neural foramen, through which the spinal cord and nerve roots of the lumbar (lower) spine pass, caused by the degeneration of the lumbar discs (through fluid loss and collapse) and the facet joints of the spinal column. In lumbar spinal stenosis, the lumbar discs deteriorate and the lumbar disc spaces collapse, resulting in a portion of the lumbar discs protruding into the ventral or anterior (front) portion of the spinal canal. At the same time, the two facet joints associated with each lumbar vertebrae become arthritic, growing in size, and protruding into the dorsal or posterior (back) portion of the spinal canal. Thus, the cross-sectional diameter of the spinal canal is decreased, impinging on the spinal cord and nerve roots of the lumbar spine. In addition, the ligamentum flavum that connect the bases of the spinous processes of the spinal column and the lamina tend to buckle with lumbar disc collapse, further decreasing the cross-sectional diameter of the spinal canal. The neural foramen, through which the nerve roots exit, are pinched with disc collapse and facet joint arthropathy. This condition is especially common in the elderly and symptoms may include remitting or unremitting pain and/or weakness/numbness in the middle to lower back and/or legs when moving and/or stationary. It should be noted that similar problems can occur in the cervical (upper) spine as well.
Conventional treatments for lumbar spinal stenosis include oral and/or injectable analgesic and/or anti-inflammatory medications (non-steroidal and/or steroidal), activity avoidance and/or physical therapy, braces, and/or surgical procedures. Surgical procedures for lumbar spinal stenosis include laminectomies/laminotomies and/or spinal fusions. In a laminectomy/laminotomy, all or a portion of a given facet joint, lamina, and ligamentum flavum are removed to alleviate compression of the spinal canal. This procedure basically “unroofs” or enlarges a portion of the spinal canal. Additionally, a spinal fusion may be performed. In a spinal fusion, a connecting bar and a bone graft are used to join or fuse adjacent vertebrae via a plurality of pedicle screws, thus stabilizing the vertebral segment. Much, if not all, of a given lumbar disc is removed in conjunction with a spinal fusion. In general, a spinal fusion is most suitable when there is instability or translation between adjacent vertebrae (spondylolisthesis). Disadvantageously, the plurality of pedicle screws used to perform a spinal fusion may become loose with the passage of time if a nonunion develops. Both laminectomies/laminotomies and spinal fusions are major, open procedures, typically requiring a relatively large incision and a general anesthetic. This may be dangerous for the elderly or the sick. In addition, both procedures are very expensive.
What has been observed clinically is that many patients, when they flex forward, experience an increase in the cross-sectional diameter of the spinal canal and neural foramen, thus alleviating or eliminating their pain and/or weakness/numbness caused by lumbar spinal stenosis. This is caused by the temporary distraction of the spinous processes and the “stretching out” of the ligamentum flavum that connect the bases of the spinous processes and lamina. The collapsed neural foramen are also increased in height and cross-sectional area by the distraction. In other words, the lumbar discs and other structures of the spinal column are temporarily decompressed. This observation has led to improved treatments for lumbar spinal stenosis, for example.
In this lumbar spinal stenosis example, it is desirable to develop devices and surgical methods for distracting adjacent spinous processes, or the laminae at the bases of the adjacent spinous processes, apart. It may also simply be desirable to stabilize these adjacent spinous processes, or the laminae at the bases of these adjacent spinous processes, in the treatment of other conditions. It may further be desirable to distract and/or stabilize a spinous process, or the laminae at the base of the spinous process, with respect to the sacrum of the spine. In each case, both static and dynamic devices and surgical methods are desirable. Thus, what are needed in the art are such vertebral stabilization devices and associated surgical methods.